August 2017 - Report and Summary

by Robert K. Peters, Ph.D. - National Weather Service Cooperating Observer

The month of August 2017 was the wettest August on record. It also saw slightly below normal temperatures. The 11.66 inches of rainfall very little of which fell with Hurricane Harvey easily surpassed August 1915 which held the existing record of 10.25 inches. The Summer of 2017 was the second wettest on record with 21.45 inches. The Summer of 2007 saw 23.35 inches.

Despite a cool August, June and July saw above normal temperatures. As a result, the Summer of 2017 was 0.4 deg. Warmer than normal. The thirty-day outlook for August 2017, issued on July 20, had called for above normal temperatures and near normal precipitation. When revised on July 31, it called for below normal temperatures and above normal precipitation. Compared with August 2016, the month was 2.4 deg. Cooler and 7.83 inches wetter. Year-to-date rainfall was 12.07 in. Greater in 2017 than in 2016.

August began and ended very unusually. An upper air trough extended southward from the Aleutians, with a ridge meridionally oriented along the Pacific Coast, and a trough over Eastern North America. This meant that winds down the Plains were northerly, transporting periodic cold fronts and upper air disturbances. The result was below normal temperatures and periods of showers.

A front crossed on the night of the 1st-2nd. This resulted in widespread rains of one to three inches, with coverage near 90 percent. The heaviest rain from this event was 5.27 inches at Carthage. Tyler established a new August 2 rainfall record with 2.99 inches. Coverage of showers was under 30 percent on the 3rd and 4th, but increased to near 50 percent on the 5th with another weak front. There was a decrease on the 6th, with an increase to more than 80 percent with the front of the 7th. This latter feature brought rains of between one-half and two inches, with four or more inches along Red River. Wright Patman Dam received 7.71 inches and Bonham 6.17 inches.

The weak upper air high built back over the region between the 9th and 12th. This warmed temperatures, but was not strong enough to suppress scattered showers each day. These were most numerous on the 11th because of another weak cold front which entered the region from the north.

The heaviest rains came on the morning of the 13th, with amounts running from around one-half inch in the south to between six and eight inches in Hunt and Hopkins Counties. Coverage was near 80 percent. The heaviest was 8.20 inches at Sulphur Springs. The rains were the result of yet another cold front and upper air disturbance. Tyler set another daily rainfall record on the 13th with 2.54 inches. Weak upper air high pressure built into the region between the 14th and 16th. There were a few isolated showers each day as temperatures warmed to slightly above normal.

Another cold front and upper air low crossed on the 17th. Tyler set its third daily rainfall record for August on that day with 3.52 inches. The ridge continued in place for the next few days, with only isolated to widely scattered showers through the 22nd. Temperatures were near to slightly above normal, though there was a slight decrease in daytime temperatures on the 21st due to the loss of heating and energy from that day's partial solar eclipse.

A cold front passed through the region on the 23rd, lowering temperatures, and bringing widespread showers on the 23rd and scattered activity on the 24th. The heaviest rainfall on the 23rd was 3.33 inches at Crockett, with most amounts area-wide running from around one-half inch to two inches.

. . . and then came Harvey!

Harvey formed as a tropical depression in the Western Caribbean Sea on the 17th, crossed the Yucatan on the 20th and weakened, but re-intensified over the southern Gulf of Mexico on the 23rd. He came ashore as a Category 4 hurricane at Rockport on the evening of the 25th, weakening to a tropical storm on the 26th as he made a slow circle between Victoria and San Antonio before re-emerging over the Gulf of Mexico at Port O'Connor on the 28th.

In this second landfall over Texas, rains of between one and twenty inches occurred south of US-79 between the 26th and 30th, with much lighter amounts north of that line. The presence of clouds and rain with the moderate northeast winds associated with the storm lowered temperatures to 5-10 degrees below normal between the 26th and 30th. A gauge in League City (southeast of Houston) measured 51.88 inches, and the Beaumont-Port Arthur airport received 22.33 inches on the 29th nearly half that station's storm total of 47.35 inches.

In East Texas, Zavalla received 20.25 inches and the Sam Rayburn Dam 18.47 inches for the heaviest amounts. Tyler received 0.15 inch, and Longview 0.73 inch. Temperatures began warming back closer to normal on the 31st with the final eastward departure of the storm.

KEY TO SYMBOLS:

A = HAIL

B = BLOWING

D = DUST

F = FOG

H = HAZE

IP = SLEET

K = SMOKE

L = DRIZZLE

R = RAIN

S = SNOW

T = THUNDERSTORM

Z = GREENWICH MEAN TIME

ZL = FREEZING DRIZZLE

ZR = FREEZING RAIN

- = LIGHT

+ = HEAVY

The reporting period for temperatures and phenomenon on each day is for the twenty-four hours ending at midnight hours GMT--6 p.m. CST and 7 p.m. CDT. The reporting period for precipitation is for the twenty-four hours ending at noon GMT--6 a.m. CST and 7 a.m. CDT. All times are given using the twenty-four hour clock, and are expressed in Greenwich Mean Time.

Observations are from NWS Station 41/9207/4 in Tyler, Texas. The term "normal" refers to averages from the standard climatic period 1971-2000.